For spells of this Champions League qualifier, Dundalk were back to their best. But it was a brief return to their worst that cost them a precious win.

Stephen Kenny's side made an unwelcome habit of conceding poor goals in the 2016 run that really put them on the map at European level.

Irish sides can just about handle wealthier opponents hurting them with moments that showcase their quality. With Dundalk, the wounds often seem to be self-inflicted.

That was the case here with a painfully soft concession just before the interval letting Rosenborg off the hook and giving the Norwegian champions a draw that they seemed quite satisfied with in the dying stages.

It sets up another tense, high-stakes affair in Trondheim next Wednesday with Rosenborg's excellent home record giving them every reason to be bullish about their prospects in the decider. Coach Kare Ingebrigtsen declared it a good result.

The flip side of that is that Dundalk have a knack of scoring on their travels and will go there in the knowledge that repeating the dose would swing the pendulum their way.

Dundalk's David McMillan in action against Rosenborg's Johan Laerdre Djordai. Photo by David Maher/Sportsfile

"Rosenborg are a good side," said Kenny. "But we have shown we have the capacity to score goals."

He duly pointed out that last term's adventure also kicked off with a 1-1 home draw with Icelandic side FH, although he conceded that Rosenborg are a good bit better and will have a packed stadium behind them.

The topical encouragement for Kenny is that his charges appear to be back on track following an erratic start to the domestic campaign which has ended any hope of retaining their league title with Cork well on the way to a coronation.

Before kick-off, Dundalk's PA announcer boldly predicted another spectacular European night and the white shirts started off with the purpose to make it so.

Dundalk's David McMillan reacts after his shot went wide. Photo by David Maher/Sportsfile

They were ahead inside 20 minutes and it was thoroughly deserved with a tentative Rosenborg side standing off Dundalk and allowing the hosts to get into the rhythm.

It would have been an understandable tactic if their rearguard was tight enough to absorb the pressure, but Rosenborg have leaked goals recently and that weakness was apparent as they were slow to track runners. Robbie Benson might even have scored inside a minute.

Pressure paid off when Dundalk's left winger Michael Duffy, a bright presence in the early stages, wandered inside after a good passing move and shaped for a right-footer that started off like a shot but ended up functioning as a perfect cross with David McMillan predicting the flight and directing a header past Andre Hansen.

The Dundalk striker was registering his seventh Champions League qualifying goal in the space of three seasons.

It gave Dundalk a deserved advantage, although the high-intensity start took its toll and Rosenborg began to threaten. Gary Rogers made a pair of stops to deny a deflected Nicklas Bendtner effort and a close-range strike from Pal Andre Helland.

Benson, Chris Shields and Patrick McEleney were given plenty of time to spray the ball around in the middle with Rosenborg not working hard enough at times. However, Dundalk lacked real assurance at the back with Niclas Vemmelund, tasked with tracking his higher-profile compatriot Bendtner, guilty of a few stray passes that angered Kenny.

He was duly given serious cause to lose his temper. Rosenborg are good from set-pieces, sending forward the cavalry at every opportunity, but their leveller a minute shy of the interval didn't even come from a particularly skilful execution.

After a contested foul, a free was swung into the area where big centre-half Tore Reginiussen was lurking unmarked, and a combination of his efforts and the backtracking Brian Gartland carried the ball past Rogers. Kenny said his man felt he got the final touch.

For Rosenborg, it was bonus territory. They had played poorly and still effectively had the advantage with an away goal.

From the resumption they were sharper initially, applying pressure further up the park. A break from their skipper Mike Jensen drew a save of real quality from Rogers. But the scoreline gave them a position to protect.

"Their goal changed the game because they could sit in and commit no players forward," said Kenny.

With half an hour to go, he was forced into a sub with injury ending Vemmelund's participation and Paddy Barrett coming in. Strangely enough, Barrett was also called in as an emergency sub in Dundalk's first joust with FH a year ago.

The delay in Barrett's introduction riled up the locals with Bendtner misreading his team-mates' intention to give the ball back when Rogers booted the ball out of play. It injected a bit of life back into the venue and pressure followed with McMillan heading over a corner and the guests falling back a little bit further again.

Their application was better in the second half, and there were phases where Dundalk owned the ball without really penetrating. Rosenborg sporadically threatened on the counter..

Kenny sent for new recruit Dylan Connolly in an attempt to break the game, but his inexperience was apparent and this game was a bit too congested for the ex-Bray man to showcase his blistering pace.

"There wasn't much space behind them and we had to score from a cross," admitted Kenny.

The Lilywhites kept trying to chip away and a late rally provided dead-ball situations but Rosenborg saw them out comfortably enough to take a result that looked unlikely until Dundalk's lapse of concentration.

"This game is still very much in the balance," asserted Kenny.

"I wouldn't get fixated on the away goal. Their home form is good and 1-1 suited them, but we are dangerous ourselves.

"There is still a match to be played and we are still level. It's very rare you get a 0-0. There is still a game to be won."